Block copolymers contain chemically distinct polymer chains (blocks) covalently linked to form a single molecule. Block copolymers may exhibit chemically directed self assembly to form different structured morphologies, such as cylindrical morphology, gyroid morphology, or lamellar morphology. Owing to their mutual repulsion, dissimilar blocks within the molecule tend to segregate or phase separate into different domains, the spatial extent of the domains being limited by the constraint imposed by the chemical connectivity of the blocks. From an entropic standpoint, the molecules may prefer random coil shapes, but the blocks may be stretched away from the interface to avoid unfavorable contacts. As a result of these competing effects, self-organized, structured morphologies emerge on the nanoscopic length scale. Various microdomain structures can be achieved, depending on relative volume ratio between blocks and chain architecture, as well as the chain lengths of the respective blocks. These microstructures may satisfy the size requirement for many potential nanotechnologies.
Nanometer scale patterns based on self assembly of block copolymers have been considered as alternatives to replace or augment high resolution lithographic technologies. In particular, self assembly of block copolymers has received attention because of the scale of the microdomains (e.g., on the order tens of nanometers), their various chemical and physical properties (e.g., differential etching rates) and the size and shape tunability of microdomains afforded by changing the molecular weights and compositions of the blocks making up the copolymers. As a “bottom up” molecular system, block copolymer lithography allows some control over the size and the two-dimensional arrangement of nanoscale features. By changing the molecular weight, and/or the relative ratio of constituent blocks, the morphology and size scales of the features can be controlled. In terms of thin films, the nanoporous materials derived from block copolymers have also been studied as nano-templates, membranes, separation media, high surface area support for catalysts, and sensors. The self assembly of block copolymers has been considered as a route to nanostructured materials and has led to the development of block copolymer lithography as a technique used in fabricating microelectronic devices.
However, the use of block copolymers in lithographic technologies suffers from the drawback that for each morphology and size of the feature desired, a different block copolymer must be synthesized because the molecular weight and/or relative ratio of constituent blocks must be changed.